Titanium, that exhibits very high corrosion resistance in the atmosphere, is used in building applications such as roofs and walls in seacoast areas. Although more than ten years have passed since titanium began to be used for roofs and other building materials, no cases of corrosion have ever been reported. However, the surface of titanium, depending on service environment, sometimes becomes a dark golden color during long use.
Though this discoloration is limited to the very shallow surface and, therefore, does not impair the anti-corrosive function of titanium, it sometimes gives rise to problems when titanium materials colored by interference color are used for their ornamentality.
Because of their ornamentality, titanium materials colored by the interference color are also used in applications other than outdoor ones. Because coloring is based on the interference action of oxide films, smudging with finger prints or oily stains makes the smudged part appear to have a different color tone and is noticeable.
To prevent the environment-dependent discoloration mentioned first, Japanese Unexamined Patent Publication 130886 of 1998, for example, discloses a method to prevent discoloration of titanium materials by specifying the structure of oxide films on them.
“Surface Treating Measures Q and A 1000” compiled by the Surface Treating Measures Q and A 1000 Editorial Committee (page 634, published by Sangyo Gijutsu Service Center Co., Ltd. In May 1998) depicts a method to prevent surface discoloration, deterioration and contamination by applying transparent coatings. However, this document also says that “this method sacrifices the color of interference coating in preventing contamination and, therefore, no methods to prevent surface contamination without losing the color of interference coating have ever been established.” Contamination can be also prevented by sandwiching a titanium sheet between sheet glasses by way of adhesive layers. However, the surface of titanium sheets sandwiched between sheet glasses are similar to that of titanium sheets covered with transparent coating. Therefore, the interference color is impaired as in the case of titanium sheets covered with a transparent coating.
Laminated glasses are manufactured by inserting one or more strong transparent synthetic resin films between two or more sheet glasses, with application of heat and pressure. When laminated glasses break, the strong synthetic resin film prevents shattering of glass and provides safety. When laminated glasses are hit, the strong synthetic resin films do not allow the penetration of the hitting object and, thus, prove effective in crime prevention. Because of these advantages, laminated glasses are widely used for windows, doors and other applications in automobiles and other transportation facilities and buildings.
Laminated glasses sandwiching sheets of paper or cloth or metal foils between two or more sheet glasses to enhance ornamentality are also proposed (as in, for example, Japanese Unexamined Patent Publication 12456 of 2002 and Japanese Unexamined Utility Model Publication 47339 of 1994). Inserting sheets of paper or cloth or metal foils between sheet glasses provide higher ornamentality to laminated glasses by permitting the degree of transparency (including semitransparency and opaqueness), color and pattern to be variously altered depending on use.
Titanium is used for roofs, walls and other building materials in coastal regions as they exhibit very excellent corrosion resistance in the atmospheric environment and titanium colored by the interference color has high ornamentality because of the vivid colors that change with the angle of view. Although more than ten years have passed since titanium began to be used for roofs and other building materials, no cases of corrosion have ever been reported. However, the surface of titanium, depending on service environment, sometimes becomes a dark golden color during long use.